Energy brings countless benefits to us. However since few years ago, abnormal temperature phenomena of earth such as cold weather and heavy snow, heavy rain and drought, landslides, hurricanes, heat waves, etc, are seriously breaking the highest records of earth's history and it is being concluded that the cause of such extreme weather anomaly lies in the global warming phenomenon due to the use of fossil fuels.
Various nations in the world have recognized such reality and are investing a great deal of capital to develop cleaner fuels for the future. Also, along with various efforts to find the unlimited energy to escape from the dependency on fossil fuel, in other words the future energy, researches and developments are thoroughly conducted for finding new energy sources that can replace the oil and the coal in order to resolve the energy issue.
New energy sources that the human should pursue after departing fossil energy includes many types of energies such as the solar energy, the wind power energy, the artificial sunlight, the hydrogen energy, the energy using the sea water, the bio energy. Just as other energies, the wind power draws attentions as a new energy source for the future for its environmental friendly and renewable characteristics and has the advantage of being enabled to generate electricity for 24 hours a day as long as the wind is blowing, while the solar generation is limited by cloudy climates and nighttimes. Since the wind is unlimited and clean natural element, the wind power energy is recognized for its value as an alternative fuel which does not produce air pollutions or dangerous wastes. Although the wind power generation has sufficient possibility as an alternative way of generating power, the wind power generation in the low wind velocity region cannot completely replace the role as the self generator (power generation for self-consumption) or as the effective capacity of resource that react as the spinning reserve for its power generation capacity credit due to the wind variability where the wind suddenly changes directions and due to the wind energy having a low wind speed (2˜6 m/sec), thus the development of economical and highly efficient wind energy electricity generator for low wind velocity for distributed power grid system is urgently required.
In case of installing the wind power generator for the rated wind velocity of 12 m/sec in a low wind speed region where the annual average wind velocity is 2˜6 m/sec, the system includes either a large generator of excessive capacity of 4 or higher folds or a small to medium generator still having an excessive capacity so the loss of investment is too significant. Since the generation capacity of Vestas in Denmark and other world famous manufacturers are manufacturing their products with the rated wind velocity of 12 m/sec, their products are not productive in the low wind velocity environment.
Furthermore, in the region of low wind velocity, the direction of the wind is not unformed and frequently causes yawing so the efficient generation cannot be achieved.
In the region of low wind velocity where the temperature difference on the ground surface caused by the Sun and the cloud creates the wind, the wind direction changes frequently and the Reynolds number fluctuates excessively. However, it is a burden for the world to give up on the wind power resource because of the world trend of green growth which must utilize the energy from the nature. The current increase of installations of many wind power generators with high capacity in the region of low wind velocity with insufficient starting torque are based on the installation capacity to demonstrate and has a large difference from the actual investment and the amount of generated power. Therefore, such installation is considered as very unfortunate in terms of the economic analysis or the green energy development.
Therefore, the wind power generation technology optimized for the low wind velocity of 2˜6 m/sec is seriously required in order to efficiently use the wind power resource.